package/x11r7/xlib_libXfixes: fix compile error by backporting upstream commit

package/x11r7/xlib_libXfixes: fix compile error by backporting upstream commit

Fixes an error not yet caught by autobuilders:

In file included from SaveSet.c:27:0:
Xfixesint.h:67:20: error: static declaration of '_XEatDataWords' follows non-static declaration
 static inline void _XEatDataWords(Display *dpy, unsigned long n)
                    ^

To reproduce use this defconfig:

BR2_powerpc64le=y
BR2_powerpc_power8=y
BR2_OPTIMIZE_3=y
BR2_GLIBC_VERSION_2_23=y
BR2_BINUTILS_VERSION_2_26_X=y
BR2_GCC_VERSION_5_X=y
BR2_TOOLCHAIN_BUILDROOT_CXX=y
BR2_PACKAGE_XORG7=y
BR2_PACKAGE_XLIB_LIBXFIXES=y

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>